1. Field of the Invention
The present invention is directed to a process and a device for controlling power for a circuit comprising a resonant inverter.
2. Discussion of the Background
Patent application GB 2 175 154 A discloses an inverter which supplies a variable impedance load and comprises an inductive component and a resistive component. This inverter is of the resonance type and comprises a control circuit in which a first and second DC voltage, which represent respectively a peak value and a cyclic ratio of currents circulating in transistors of the inverter, are applied to the inputs of an amplitude comparator, the output of this comparator serving to control a frequency of a switching pulse of the resonant circuit.
This type of inverter is used, in particular, in induction cooking plates, the load then comprising an inducer and a cooking utensil set on the inducer. In this case, the power control of the inverter is an open loop control as long as the current in the transistors of the inverter itself is not greater than a given value.
With this type of control circuit, it is realized that, when saucepans are made of different materials but with the same diameter, they are going to receive a different power. Furthermore, it is desirable that between two utensils of different diameter, the one whose diameter is smaller consumes less power. It is therefore difficult to regulate properly the power of the induction cooking plates. Actually, during the manufacture, the power for a given saucepan will be regulated with a form factor of the given line voltage but then when other saucepans or another form factor of the line voltage is used, the desired power is not exactly obtained.